1. Field of the Invention
The present invention relates to a process for producing dichloroacetaldehyde hydrate together with chloral from acetaldehyde or para-aldehyde.
2. Description of the Background Art
Dichloroacetaldehyde (hereinafter abbreviated as DCA) is a compound useful as a raw material for the synthesis of drugs and agricultural chemicals. Because this compound is extremely unstable, it has been supplied as an aqueous solution. In the past, hydrate of DCA was manufactured by the method of chlorinating 1,2-dichloroethylene using a method described, for example, in Deutsche Offenlegungsschrift 2306335. This method is not practiced at the present time, because 1,2-dichloroethylene is obtained only with difficulty.
Chloral, on the other hand, is manufactured by the chlorination of acetaldehyde or para-aldehyde. DCA is known to be produced in the course of this chlorination process. The process, however, cannot produce DCA alone; DCA is obtained together with monochloroacetaldehyde and chloral which have chlorination degrees different from that of DCA. Boiling points of these chlorinated acetaldehyde compounds are very-close to each other. No method has been known to efficiently separate DCA from the mixture. Because of this reason, the production of DCA by the chlorination of acetaldehyde or para-aldehyde has not been practiced.
In view of this situation, the present inventors have undertaken extensive studies with an object of developing a process for producing DCA hydrate from raw materials which are available at low costs, and completed the present invention, by which DCA can be produced as a hydrate together with chloral from acetaldehyde or para-aldehyde.
As a result, the present inventors have found that high purity DCA hydrate crystals can be obtained if a mixture of chlorinated acetaldehydes with different chlorination degrees, which is obtained by the chlorination of acetaldehyde or para-aldehyde (hereinafter these are collectively called raw material aldehydes), is crystallized under specific conditions, and that the remaining raw material aldehydes can be effectively utilized by converting them into chloral hydrate. These findings have led to the completion of the present invention.